<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>事件</title>
</head>
<body>
    
    <button id="btn">click me</button>

    <script>
    
        let oBtn = document.getElementById('btn');
        oBtn.onclick = function (e) {
            console.log(e.data);
        }

    </script>

</body>
</html>